Control room redesign

[J.J.McLeod]

How thick is the glass in the sliding door??

I haven't measured it, but it's pretty flimsy and certainly isn't airtight. I was thinking of replacing it with a solid core one if I faced south.

I don't believe the extra ceiling height should effect the low end as much as you say it varies. I suspect both doors.

Hope you're right. Guess that means the ceiling tiles stop the bass pretty well.

But if there is that much variation why not stay where you are?? at least you can see into the booth:) You could build a reciprocal wall on your right to match the booth window wall and build another wall across the north end to create symmetry.

That was actually my first plan (not posted), but I thought it would make the room too small and short. One variation was to move the south wall 4' further south, and to convert my alcove into the hall. However, where I am now might be worse (see phase problems below), although maybe the south wall mirroring the shape of the booth wall would fix it.

I really think you are in need of more acoustic treatment generally.

No doubt about that I was just hoping to make the room more symmetrical, too. What worries me is how out of phase the two monitors are (and even one monitor in two places).

Panning the recorded output of the monitors hard left/right and running them through a phase torch shows some wicked anti-phase in both positions. At the proposed south wall location the two are out of phase at 82Hz and the entire range between 120-136Hz. The signal actually progresses counterclockwise through the anti-phase and reaches the top again around 160Hz. Remember that the monitors were equidistant from all three walls and drop ceiling in the vicinity.

My current position is worse. It has the same problem over two ranges - 87-120Hz and 161-178Hz. Notice how the response at the two positions are the opposite of each other? I also performed the same test in a supposedly well-designed symmetrical room, which has problems because of the all-dead acoustic treatment, but almost never goes into anti-phase and is much more consistent. These phase issues seem to be realtively independent of the volume differences between the two monitors - although, of course, they affect the volume of the summed signal a lot.

So I might still want to turn south, but I'd be bummed if it turned out that the difference in the height of the shell made it impossible to have symmetrical bass. What do you think of the phase problem anyway? Is this normal? I'm thinking that no amount of absorption at these frequencies would fix the problem, so symmetry is key.

Thank you so much for your patience and help! BTW, I can't give you Bush's head on a platter because the line's too long and the platter would be really big (or maybe really small)

Thanks!

J.J.

J.J. McLeod
Different Drummer Studios
www.differentdrummerstudios.com
[/quote]

[John Sayers]

Hope you're right. Guess that means the ceiling tiles stop the bass pretty well.

No the bass would go straight through them but it still shouldn't cause out of phase components.

Panning the recorded output of the monitors hard left/right and running them through a phase torch shows some wicked anti-phase in both positions. At the proposed south wall location the two are out of phase at 82Hz and the entire range between 120-136Hz.

I'm not sure what you are doing here - recording them with what and how?? ...could you elaborate??

cheers
john

[J.J.McLeod]

I used Pro Tools' signal generator plugin to play sine waves in 4Hz increments betweeen 20-300Hz. I recorded the result as audio so it never changes. I then recorded the output of the monitors alone and together with an Audio Techinica 4050 (no Earthworks at the moment) in Omni mode, no hi-pass, etc., at the mix position. Pan them hard left and right and look at the result in a phase torch plug-in (circular, X/Y grid).

Duplicating the track with the orginal tones and hard panning the original left and the duplicate right shows perfect unchanging phase. Comparing the monitors on the south wall to each other shows them to rarely be completely in phase but almost totally out of phase in the range of 120-136. The output at my current position has much larger sections of the bass spectrum out of phase between the two monitors as noted before. You can hear it in headphones, too.

Interestingly, comparing one monitor's output - or both together - to the original file (after time adjusting) shows that the phase constantly/sluggishly rotates counterclockwise as the tones rise in pitch. This is true in my room and the other control room I tested. What's different between the two rooms, however, is that the monitors are out of phase with _each other_ in my room, whereas the other room is much more phase-coherent throughout the range I tested. In both rooms phase between the two monitors improves above 200Hz or so.

Thanks,

J.J.

J.J. McLeod
Different Drummer Studios
www.differentdrummerstudios.com

[J.J.McLeod]

No the bass would go straight through them but it still shouldn't cause out of phase components.

O.k., but forgetting phase for a moment, would the bass escaping above the east monitor account for less cancellation compared to the west one, or does the bass from the west monitor go up there, too? The east one had quite a bit more bass overall, usually 3-8db (although at a few frequencies it was the opposite), so it seems like the west one had more cancellations from bass buildup. In fact, at 186Hz (which doesn't seem to correspond to a node), the west one had a dip that was 16db quieter than the east monitor. Of course as you mentioned, it might be caused by the doors.

Sorry for all the questions. Just measuring twice and cutting once.

Thanks,

J.J.

J.J. McLeod
Different Drummer Studios
www.differentdrummerstudios.com

[John Sayers]

JJ you are chasing your own tail. You've got a room that has no apparent acoustic treatment and you are finding ambiguities in the rooms response. You would expect that which is why you need to look at proper room acoutic treatment - that's why people treat their rooms.

cheers
john

[J.J.McLeod]

Understood, but it's not clear that this would fix the asymmetrical response I'm getting. Does the addition of symmetrical bass trapping in a room suddenly erase 8-16db differences in bass response between two monitors? It seems that bass trapping would reduce the problem, but the source of the asymmetry is elsewhere.

My concern is that even with more treatment, and even with the doors moved to more acoustically neutral locations, the difference in "real" ceiling height would still make the two sides noticeably asymmetrical if I faced south. I'm worried about spending hundreds/thousands of dollars and seeing little improvement in symmetry, which is why I'm asking experts for their opinion.

I read a lot of audio/recording forums almost daily, but this is the first one I've posted to in years because I respect your opinion and believe that acoustics is more important than all the gear in the world.

I know that my place has problems acoustically, and I'd abandon it in a second except for the fact that there's built-in work from next door. Not enough work to justify a massive overhaul, but enough that I need to fix the acoustics as best I can. So I'm stuck with finding a solution that's the best compromise between sound quality and price.

I plan to build bass traps per your specs once I understand the details better. You've convinced me that Ethan's bass traps might not be the ticket, and that slot absorbers and hangers are the way to go. But saying that a room with 703 panels covering almost every vertical surface has "no apparent acoustic treatment" seems a little harsh, don't you think?

Thanks again for your patience and understanding

J.J. McLeod
Different Drummer Studios
www.differentdrummerstudios.com

[John Sayers]

But saying that a room with 703 panels covering almost every vertical surface has "no apparent acoustic treatment" seems a little harsh, don't you think?

I'm sorry JJ - I didn't realise that that was your situation with the 703 - I thought you were about to add treatment.... My Bad.

Could you describe the ceiling structure in a bit more detail - your drawing doesn't quite give a realistic picture I syour room open to the higher ceiling over the rest of the building??

cheers
john

[J.J.McLeod]

I'm sorry JJ - I didn't realise that that was your situation with the 703 - I thought you were about to add treatment.... My Bad.

No worries I consider myself fortunate to still have your attention after so many long posts!

My control room has a drop ceiling over the entire length and width of the room. The bottom of the second floor is above that about 2' higher and runs the entire 20' length, but the width of the second floor only runs for 10' west to east. So the eastern 3' above the drop ceiling is open to the ceiling of the building, which is at least 15 feet above the drop ceiling. This back area used to be a warehouse space, and we've often thought of using it for a larger live room eventually. In my first post, the final drawing shows this visually. The ceiling in control room A is the drop ceiling, then the second floor is above it. I'm worried that bass escaping through the drop ceiling on the east side makes the east and west sides assymetrical in the bass. But if I closed it off, more bass would be trapped in the room, making the bass problem even worse.

The subject of the drop ceiling is even more complex because I'm still trying to figure out the best way to treat it. If I try to hang 703 from the entire drop ceiling I'm afraid the drop ceiling frame won't support it. What do you think? What about the possibility of replacing the ceiling tiles with 4'x2' rectangles of 703?

Otherwise I'd have to hang them from the bottom of the second floor, which means getting rid of the drop ceiling and closing off the eastern gap in the "hard ceiling" with drywall. At that point, maybe it would make more sense to use hangers and a false cloth ceiling, and take the 6" fluffy insulation that's currently on top of the drop ceiling and attach it to the bottom of the second floor ("hard" ceiling) for high frequency absorption. It depends, I guess, on whether a 2' gap is big enough for hangers. What do you think? Would hangers, say, 18 inches by 8 feet have enough mass for at least some upper bass absorption?

Also there would be some challenges with air ducts since they're above the drop ceiling, but hopefully I can figure that out on my own.

One more problem with getting rid of the drop ceiling is that the ceiling would then be 10', or half the 20' length of the room. Since this room is mostly rectangular, room nodes do seem to have an effect. On the other hand, if the bass is passing right through the drop ceiling, maybe I already have a 10' ceiling as far as bass is concerned. And if I put hangers in the 5' deep alcove at the north end of the control room, maybe the room acts as if it's 15' long...

I think I 'm getting dizzy. As you can see, you've got me thinking a lot about acoustics.

Many thanks!

J.J.

J.J. McLeod
Different Drummer Studios
www.differentdrummerstudios.com

[John Sayers]

As you can see, you've got me thinking a lot about acoustics.

Well that's good

I'd close off that huge cavity up there first. You can then treat the bass once it's contained.

You could hang false ceiling panels by chains that go through the drop ceiling and attach to the actual ceiling. These could have a plywood backing on a 4" x 2" frame with 703/cloth on front. (clouds as they are sometimes called) They could then be angled with the chain length to break up the floor/ceiling parallels.

Yes hangers in the rear would help a lot, and the room would still be 20ft. You could copy the angle of the booth window on the opposing side also.

cheers
John

[J.J.McLeod]

I'd close off that huge cavity up there first. You can then treat the bass once it's contained.

Thanks. Not the answer I was hoping for, but pretty much the same conclusion I had come to.

So about the clouds - do you think I need to keep the drop ceiling to keep the height at 8' for node reasons? Otherwise between construction on the "gap" and trying to cut holes for the chains for the clouds and the hangers in the back I think I'd rather get rid of the drop ceiling altogether. If the nodes are the reason, then maybe another wall in the hanger area to make the length, say, 18 feet? That would still leave 3ft. for hangers.

Thanks again. I'm almost done with this thread. Soon I'll just be asking annoying bass trap questions!

J.J.

J.J. McLeod
Different Drummer Studios
www.differentdrummerstudios.com

[J.J.McLeod]

Let me rephrase the question. Ethan's acoustics faq:

www.recording.org/users/acoustics

says a drop ceiling is basically transparent to room nodes, and the hard ceiling above is the real boundary of the room for node calculations. Do you agree? If so, my drop ceiling's days may be numbered, and maybe hangers in a false ceiling would be the way to go.

Thanks,

J.J.

J.J. McLeod
Different Drummer Studios
www.differentdrummerstudios.com

[John Sayers]

Yes the drop ceiling is transparent - I think I said that before. But it does hide all the aircon ducting you mentioned.

The solution I proposed with the clouds is the cheapest and easiest way to break up the floor/ceiling parallel surfaces. You can always remove the individual ceiling panels, put your hangers in and then put them back, getting the best of both worlds, or you can just remove them permanently above the clouds and just put hangers there therefore retaining a clean ceiling line where the clouds don't cover the ceiling

cheers
JOhn

[J.J.McLeod]

Thanks, John. I really appreciate your help throughout this long, convoluted thread.

J.J.

J.J. McLeod
Different Drummer Studios
www.differentdrummerstudios.com